An interesting characteristic of virtually all materials is their strain-rate sensitivity. In the case of engineering thermoplastics, these materials exhibit ductility and very good impact resistance at low to average strain rates (<10 %/sec) but can become extremely brittle and unforgiving at high strain rates (100 - 5.000++%/sec). This becomes a concern in energy management applications, such as automotive instrument panels and knee bolsters, because, for example, the average head impact on an instrument panel induces a 1,000%/sec strain rate.
Engineering analysis of the impact event typically under-predicts loads and over-predicts deflections. Making material substitutions within a design may be of little use since the newcandidate may be more strain-rate sensitive than the original polymer. Many of the most widely specified engineering thermoplastics behave very differently in standardized ASTM “static” tests than in high strain-rate situations. Therefore, it is difficult, if not impossible, to accurately estimate performance based on extrapolated low-strain data.
Responding to a need for accurate data measured at high strain rates, and recognizing that very few organizations are equipped to perform such testing, GE Plastics and Davidson Instrument Panel have initiated a research program with the University of Dayton Research Institute (UDRI) to characterize the strain-rate sensitivity of common grades of polycarbonate (PC), acrylonitrile butadiene styrene (ABS), polycarbonate/acrylonitrile butadiene styrene (PC/ABS), polybutylene terephthalate (PBT), polycarbonate/polybutylene terephthalate (PC/PBT), and modified-polyphenylene ether (M-PPE) resins.
This paper will disclose the results of the high strain-rate material testing (up to 5.000 %/sec) and resultant performance of these materials. Discussion will center around how engineers can use these data to better predict material behavior in complex assemblies.